FIELD OF THE INVENTION
The present invention relates to a radar apparatus for use in an automobile which measures a distance from an object located forward of the vehicle in the same traffic lane, and generates a first alarm if the distance is shorter than a first alarm distance and a second alarm when the distance becomes shorter than a second alarm distance.
Recently, some types of radar apparatus for use in an automobile have been proposed to avoid a dangerous traffic collision accident on a highway due to driving asleep or inattentive driving.
FIG. 1 is an explanatory view showing a situation where a laser type radar 3 as a vehicular radar apparatus of this type is assembled on a and measures a distance D between an automobile 2 traveling forward in the same traffic lane. As shown in FIG. 1, the laser type radar 3 is provided with a head 3-1 having beam irradiating and receiving sections. A laser beam LS irradiated from the beam transmitting section is reflected by a reflector 4 such as, for example, a rear tail lamp on a rear side of the forward-moving automobile 2, and the reflected beam LR is received by the beam receiving section. The laser type radar 3 calculates a distance D on the basis of an irradiation timing of the laser beam LS and a reception timing of the reflected laser beam LR, and displays the calculated distance D on a display unit 3-2 mounted in front of the driver's seat of the truck 1 as shown in FIG. 2. The display unit 3-2 is provided with a distance displaying section 3-21 which displays in format the calculated distance D which changes momentarily.
When the truck 1 comes close to the automobile 2 and the distance D becomes shorter than a safety distance (first alarm distance), an alarm lamp 3-22 turns on and a first alarm phrase is generated at the same time. If the distance D becomes shorter than a certain distance which is shorter than the first alarm distance, e.g., shorter than a half of the first alarm distance, a second alarm is generated.
The above operation will be described with reference to FIG. 3.
FIG. 3A is a timing chart showing a condition where the distance D varies (shortens) over time t, FIG. 3B shows the timing of the generation of the first and second alarms, and FIG. 3C shows a condition of the alarm lamp 3-22. When the distance D becomes less than a first alarm distance D1 at a time t1, an acoustic phrase A (a chime melody) is first generated and then an acoustic phrase B (a warning signal) is generated repeatedly. Next, when the distance is further reduced to less than a second alarm distance D2 at time t2, an acoustic phrase C (the chime melody issued two times) is first generated as a second alarm and then an acoustic phrase D ("Danger!") is generated repeatedly.
While generating the second alarm phrase, the second alarm is paused if, for example, the distance D rapidly becomes larger than the safety distance D1 at a time t3 as shown in FIG. 3, that is, if the automobile 2 traveling forward in the same traffic lane rapidly changes the traffic lane. After that, if the distance D from a different automobile traveling forward in the same lane becomes lower than the safety distance D1 at a time t4, the first acoustic alarm is again generated and, further, the second acoustic alarm is again generated if the distance D becomes shorter than the second alarm distance D2 at a time t5.
According to the conventional laser type radar apparatus 3 thus operating, the first acoustic alarm is meaningless if a time period T1 between the time t3 when the second alarm is paused to the time t4 when the first alarm is again started is relatively short.